Exhaust gas purifying system and abnormality determining method therefor

Abstract

An exhaust gas purifying system includes a catalyst arranged on an exhaust pipe of an internal combustion engine; a sensor detecting a state of the exhaust gas passed through the catalyst; and an ECU functioning as an abnormality determining apparatus determining abnormality by monitoring an output of said sensor in an operation under forced air-fuel ratio. When the operation under forced air-fuel control is interrupted before completion of the determination of system abnormality, the abnormality determining apparatus once stores a parameter accumulated during the operation under forced air-fuel ratio control by the time of interruption, and when the internal combustion engine comes to satisfy the prescribed condition again, resumes the operation under forced air-fuel ratio control, and completes determination of system abnormality using the stored parameter and the parameter accumulated after resumption of the forced air-fuel ratio control.

Description

[0001] This nonprovisional application is based on Japanese Patent Application Nos. 2005-333882 and 2006-303677 filed with the Japan Patent Office on Nov. 18, 2005 and Nov. 9, 2006, respectively the entire contents of which are incorporated by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to an exhaust gas purifying system and an abnormality determining method therefor. Particularly, the present invention relates to an exhaust gas purifying system for purifying exhaust gas of an internal combustion engine mounted on a vehicle, and to a method of determining abnormality thereof. [0004] 2. Description of the Background Art [0005] In an exhaust gas purifying system of an internal combustion engine to be mounted on a vehicle, a catalyst is arranged on an exhaust pipe, for purifying exhaust gas. The catalyst is capable of taking and storing an appropriate amount of oxygen, and when the exhaust gas contains unburned component ...

AI Technical Summary

Benefits of technology

[0017] An object of the present invention is to provide an exhaust gas purifying system in which possibility of successfully completing abnormality determination is improved.

[0026] According to the present invention, the possibility of successfully completing the process of determining whether the exhaust gas purifying system has abnormality or not can be increased.

Problems solved by technology

Therefore, when such a state continues for a long time, the catalyst eventually emits all the oxygen, and reaches a state in which oxidation of HC or CO is no longer possible.

Therefore, when such a state continues for a long time, the catalyst eventually stores the oxygen to the full capacity, and reaches a state in which purification of NOx is no longer possible.

When the engine speed or the amount of intake air frequently goes out of a prescribed range as experienced when driving through town, operating condition of the engine is unstable.

Therefore, it is disadvantageous to make determination as to whether the catalyst of the exhaust gas purifying system is normal or deteriorated, through forced air-fuel ratio control.

When the forced air-fuel ratio control is conducted while the fuel is cut, the improved mileage would be wasted.

Therefore, while the forced air-fuel ratio control is being done and the prescribed operating conditions come to be no longer satisfied, the forced control is interrupted.

Thus, it becomes impossible to complete determination as to whether the catalyst of the exhaust purifying system is deteriorated or not.

If the oxygen sensor fails, whether the catalyst is deteriorated or not cannot be determined accurately.

Therefore, it is also necessary to determine a failure of the oxygen sensor as abnormality of the system.

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